Thermal energy conversion system for regasification of cryogenic liquids

ABSTRACT

Systems and methods for cryogenic thermal energy conversion that include the use of a heat engine in the regasification process for cryogenic liquids such that energy is created while regasifying the cryogenic liquid and no additional heat component is required.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Provisional Patent Application No. 61/781,747, which was filed on Mar. 14, 2013, the entire disclosure of which is incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to systems and method for cryogenic thermal energy conversion in regasification processes. In particular, the systems and methods of the invention relate to the use of a heat engine in a regasification process for cryogenic liquids to generate energy at the traditional vaporization stage of the process.

BACKGROUND OF THE INVENTION

The current Liquid Natural Gas (LNG) market entails significant energy usage in terms of moving the desired product gas from the area of origin (often offshore or on coastal wells) to the industrialized consumer markets. At the point of source or extraction, energy, which is typically part of the natural gas product, is employed to convert the gaseous methane (natural gas) into a more convenient transport medium. In particular, this conversion typically results in medium that is about 1/600^(th) of the volume of the natural gas. The resulting medium, after pre-treatment (purification), refrigeration, and liquefaction is a cryogenic liquid (as shown in FIG. 1).

The liquefaction process first involves removal of certain components (such as dust, acid gases, helium, water, and heavy hydrocarbons) that could cause difficulty downstream. The natural gas is then condensed into a liquid at close to atmospheric pressure (maximum transport pressure set at around 25 kPa/3.6 psi) by cooling it to approximately −162° C. (−260° F.).

LNG achieves a higher reduction in volume than compressed natural gas (CNG) so that the energy density of LNG is 2.4 times heavier than that of CNG or 60 percent of that of diesel fuel. This makes LNG cost efficient to transport over long distances where pipelines do not exist. Specially designed cryogenic sea vessels (LNG carriers/Methane Freighters) or cryogenic road tankers are used for transport.

LNG is principally used for transporting natural gas to markets but is typically not the end form desired by retail consumers. After liquefying the natural gas, it is stored and shipped as a cryogenic liquid to the port of delivery whereby additional energy (again, part of the natural gas product) is employed to re-gasify the LNG so it can be distributed as pipeline natural gas to the end consumers (FIG. 2).

Both stages of LNG production and delivery—liquefaction and regasification—require significant energy and water to perform the necessary process at great expense and loss of product to create that energy. Accordingly, there is a need in the art to recover a significant portion of the liquefaction energy and remove the majority of the regasification energy requirement in LNG, liquid hydrogen, and other similar cryogenic resources so as to turn the energy recovery into a revenue-generating energy production system and maximize product delivery.

SUMMARY OF THE INVENTION

The present invention relates to a system and method of recovering the energy expended in liquefaction of natural gas and reducing/removing the energy requirement in regasification of LNG, liquid hydrogen, and other similar resources and improving overall delivery efficiencies for LNG thereby maximizing economic returns in the commercial LNG process chain.

The present invention also relates to a cryogenic thermal energy conversion system including:

-   -   a heat engine including a working fluid evaporator and a working         fluid condenser, wherein the working fluid evaporator is capable         of receiving a liquid heat source (e.g., seawater, lake water,         and the like), wherein the working fluid condenser is capable of         receiving a cryogenic liquid, and wherein the heat engine is         operable to create energy from a temperature differential         between the seawater heat source and the cryogenic liquid;     -   a working fluid suitable for optimal operation within the heat         engine under system temperatures and conditions;     -   a riser operable to deliver the seawater heat source to the         working fluid evaporator;     -   a power conduit to deliver the energy produced by the heat         engine to a predetermined destination; and     -   a pipeline to deliver regasified cryogenic product to a delivery         destination.

The present invention also relates to a regasification process for a cryogenic liquid including the steps of:

-   -   providing the cryogenic liquid at a temperature of about         −160° C. or below; providing a working fluid;     -   providing a heat engine operatively connected to a pumping         system, wherein the heat engine includes a working fluid         evaporator and a working fluid condenser, wherein the working         fluid evaporator is capable of receiving a liquid heat source,         wherein the working fluid condenser is capable of receiving a         cryogenic liquid, and wherein the heat engine is operable to         create energy from a temperature differential between the liquid         heat source and the cryogenic liquid;     -   presenting the cryogenic liquid to the heat engine and         converting the cryogenic liquid into regasified cryogenic         product;     -   delivering the energy to a predetermined destination; and         delivering the regasified cryogenic product to a predetermined         destination.

In one embodiment, the cryogenic liquid includes liquid natural gas. In another embodiment, the liquid heat source includes ambient seawater. In still another embodiment, the working fluid includes ammonia. In another embodiment, the working fluid includes polypropylene. In another embodiment, the working fluid includes other suitable refrigerants that evaporate and condense under modest system pressures between the resource delta T (about 0-35° C.) on the heat source side (seawater or lake water) and −162° C., respectively. For example, the working fluid may include Freon, an organix liquid, or a combination thereof In yet another embodiment, the working fluid includes a binary liquid (two miscible liquids with differing boiling points.

The heat engine may further include a separator and/or a recuperator. In one embodiment, the heat engine includes a Rankine cycle. In another embodiment, the heat engine includes a Kalina cycle.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention can be ascertained from the following detailed description that is provided in connection with the drawing(s) described below:

FIG. 1 illustrates the flow process of the production of liquid natural gas;

FIG. 2 illustrates a Regasification Process and the associated gas chain;

FIG. 3 illustrates a heat engine in accordance with the systems and methods of the present invention;

FIG. 4 illustrates a cryo-thermal power cycle (Rankine) in accordance with the systems and methods of the present invention; and

FIG. 5 illustrates a cryo-thermal power cycle (Kalina) in accordance with the systems and methods of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Whenever there is a large enough thermal differential between two large reservoirs (heat source and heat sink), a simple heat engine can be placed between the two reservoirs to capture the heat energy (thermal) transfer between them. Specifically, in the case of ocean-based or coastal regasification plants (or large-water based regasification systems, e.g., regasification systems based on lakes, rivers, and similar bodies of waters), there will be a significant thermal differential (ΔT) between the ambient body of water (at any depth) and the liquid cryogenic requiring regasification.

In an effort to better understand the invention and the particular benefits and applicability thereof, FIG. 2 provides an overview of a typical regasification process for LNG. In particular, Stage 1 represents the reception of natural gas. For example, natural gas is received in liquid state from the liquefaction plants, typically transported by methane freighters at a temperature of −160° C. As shown in the drawing, the LNG may be offloading from the methane freighters through transfer arms. In Stage 2, the LNG is transferred to storage tanks where the LNG is stored at −160° C. Stage 3 manages the excess generate gas by contributing heat to LNG (via a pumping process or solar radiation), which causes a fraction of the gas to pass to vapor stage. The gas (boil-off) may be used for compensating the original shipment of the LNG and reinjection into the process (after going through compressors) in Stage 4. Any remaining gas is burned in the torch. The liquefier shown in Stage 4 generally includes a primary pumping system located in the interior of the tank, which allows for the conduction of the LNG toward the liquefier. The liquefier acts as a collector of liquid for the secondary pumps (Stage 5) and allows for recuperation of the boil-off and incorporation of the boil-off into the gas flow. The secondary pumps (Stage 5) pump the LNG from the liquefier at high pressure and pushes the LNG to the vaporizers in Stage 6.

In a traditional gasification process (as shown in FIG. 2), Stage 6 represents the changeover from liquid to gas in the seawater vaporizers. The LNG is transformed into vapor by heating to a temperature greater than 0° C. The submerged combustion vaporizer shown in FIG. 2 is generally used in periods of maintenance or peak demand. In this time, the LNG is heated and vaporized with an underwater burner that uses natural gas as fuel.

One aspect of the invention substitutes or supplements the traditional seawater vaporizers with a heat engine. In particular, as shown in FIG. 3, the heat engine includes a hot reservoir and a cold reservoir. For example, a liquid heat source (e.g., warm seawater (or other types of water from lakes, rivers, and the like)) may comprise the hot reservoir and thus provide the heat source and the cryogenic liquid (LNG or similar) may comprise the cold reservoir and thus provide the heat sink to create a significant thermal differential (ΔT). This ΔT can be exploited to create significant energy for resale to the local grid or provide the regasification facility with needed energy.

In one embodiment, the system and method of the invention employs a heat engine for Stage 6 whereby the energy from the heat transfer from warm (seawater or similar) to cold (cryogenic liquid—LNG or similar) may be converted into useable energy created by the evaporation and condensation of a working fluid in a heat exchange system coupled with a suitable turbo-generator to produce the energy. For example, as shown in FIG. 4, the inventor contemplates a system and method in which Stage 6 employs a Rankine cycle or similar heat engine where the warm water enters a working fluid evaporator, at which time the working fluid is vaporized and the resulting vapor is transferred to a turbo-generator. The working fluid evaporator is operatively connected to a working fluid pressurizer such that the working fluid is transferrable to the working fluid pressurizer. In one embodiment, the working fluid pressurizer is a boiler feed pump. At the opposite end of the process, the LNG enters the working fluid condenser which is operatively connected to (1) the working fluid pressurizer such that the working fluid condensate is transferrable to the working fluid pressurizer and, ultimately, the working fluid evaporator. The working fluid condenser is also operatively connected to at least one pipeline to transfer the product natural gas vapor to the delivery pipeline.

In this aspect, the working fluid is a separate and closed loop system passing through the evaporator and condenser after passing through the turbine/generator system. The working fluid system is comprised of a working fluid (typically a refrigerant) that will boil at water resource temperatures (about 0° C. to about 35° C.) and condense under modest system pressures at the cryogenic liquid temperature (−162° C.) without freezing.

In another embodiment, the system and method of the invention employs a Kalina cycle or similar heat engine (FIG. 5). As would be understood by one of ordinary skill in the art, the use of a Kalina cycle differs from a Rankine cycle in the working fluid (e.g., a Kalina cycle employs a mixture of two fluids) and the fact that, in the Kalina cycle, the heat addition and heat rejection occur at varying temperature even during phase change, since the fluid is a mixture. For example, in this embodiment, Stage 6 may employ a cycle where the warm water enters a working fluid evaporator, at which time the working fluid is vaporized and the resultant vapor is transferred to a separator and a recuperator. The separator is operatively connected to a turbo-generator and the recuperator such that the working fluid vapor leaving the separator enters the turbo-generator and the remaining liquid working fluid enters the recuperator. The low pressure vapor exiting the turbo-generator mixes with the fluid leaving the recuperator and enters the working fluid condenser, which is also operatively connected to the working fluid pressurizer such that the resultant working fluid condensate is transferrable to the working fluid pressurizer and, ultimately, the working fluid evaporator completing the cycle. Similar to the working fluid in the Rankine cycle, a suitable working fluid (typically a refrigerant) is one that will boil at water resource temperatures (about 0° C. to about 35° C.) and condense under modest system pressures at the cryogenic liquid temperature (−162° C.) without freezing. However, the working fluid in a Kalina cycle is a binary liquid (i.e., two miscible liquids with differing boiling points).

The inventors contemplate a variety of working fluids such as ammonia, polypropylene, other organic fluids, Freon, binary mixtures of fluids, and the like that are suitable for operation and optimized for system operating temperatures and conditions.

In yet another embodiment, the system and method of the invention employs a Stirling cycle or similar heat engine in Stage 6 of the gasification process. The inventors also contemplate other forms of heat engine configurations in this aspect of the invention.

Additionally, due to the large temperature differential across the heat source and heat sink of this invention, it may be necessary to incorporate a staged step-down of heat engines (multiple stages) to accommodate a safe transfer of heat across the system and to deliver the desired gaseous product at appropriate pipeline pressures.

Regardless of the specific type of cycle and heat engine used in Stage 6 in accordance with the present invention, since the cryogenic liquid is accepting the heat and, thus, serving as the heat sink, useful energy will be created while regasifying the product LNG. As such, the present invention requires no additional heat component to the cycle, which conserves natural gas product. Accordingly, the system and method of the present invention will effectively turn what is currently an energy intensive and costly process into a revenue generating step while maximizing delivery of desired gaseous natural gas to the natural gas delivery pipeline (or similar).

In addition, because there is such a large AT dictated by the LNG delivery temperature (about −162° C.) with which to work with, this process is not limited to only the tropical or warmer regions of the world, but could be applicable at any temporal or even artic regasification station. Additionally, this would allow the extraction of the heat source water at the optimum depth to avoid current environmental restrictions and resistance to the proposed offshore regasification ships.

Currently, surface water is typically utilized in the LNG regasification systems (FIG. 2) to support the regasification water requirements, which creates environmental concerns over entrainment of critical commercial fishery larvae and early stage biology. This fact has greatly limited LNG regasification facility development offshore in U.S. waters as local environmental concerns have won over corporate interests, efficiencies and profits in recent legislation, regulation and permitting enforcement. As such, the use of deep sea water extraction for a source of cooling will significantly reduce environmental impacts currently hindering offshore LNG regasification plant development. As such, it is contemplated that the extraction of sea water at depths of at least about 500 meters as detailed in copending U.S. patent application Ser. Nos. 14/207,846, filed Mar. 13, 2014, the entire disclosure of which is incorporated by reference herein, is incorporated into the systems and methods of the present invention. In one embodiment, the extraction depth contemplated by the present invention is about 500 meters to about 1000 meters.

In another embodiment, the extraction may occur at depths of less than about 500 meters in certain latitudes and/or in certain seasons. For example, any depth below the natural thermocline (so as to avoid the region of primary productivity) would be suitable. In fact, the extraction depth may be any depth below the natural thermocline to draw from the non-productive region of the ocean. For example, in one embodiment, the extraction depth may be at least about 100 meters in high latitude locations or in mid latitude locations during winter. In this aspect, the extraction depth may be from about 100 meters to about 1000 meters. In another embodiment, the extraction depth may be at least about 200 meters. In this aspect, the extraction depth may be from about 250 meters to about 1000 meters. In addition, it is contemplated that the warmer surface water may be used to maximize energy output if environmental concerns are further mitigated or unwarranted.

In one embodiment, this invention is located offshore on a barge, vessel, ship, platform or similar and product is delivered to shore based distribution centers via pipeline or similar and the energy produced is utilized internally to run the facility or cabled to local electrical grid onshore. In another embodiment, the cryogenic energy conversion system is located in an onshore facility with pipelines delivering the necessary resource (warm) water to the facility and returned to the ambient water source slightly cooler than extracted. In this configuration, the regasified product could be delivered via pipeline to the desired distribution location via pipeline and generated electricity delivered via land cables directly to the local grid or utilized on site to provide operational energy to the LNG facility.

The systems and methods of the invention may also include a regulation system (Stage 7). For example, the natural gas from Stage 6 may be driven through a container equipped with regulation, measuring, and odorizing systems, which is then fed into the general network of gas pipelines.

It is to be understood that although the invention has been described above in terms of particular embodiments, the foregoing embodiments are provided as illustrative only, and do not limit or define the scope of the invention. Various other embodiments are also within the scope of the claims. Indeed, many modifications and variations are possible in light of the above teaching. For example, while the disclosure is focused mostly on the use of the present invention in the context of LNG, the system and method of the present invention is contemplated for use in other current or future cryogenic regasification requirements such as liquid hydrogen and other similar resources. 

1. A cryogenic thermal energy conversion system comprising: a heat engine comprising a working fluid evaporator and a working fluid condenser, wherein the working fluid evaporator is capable of receiving a seawater heat source, wherein the working fluid condenser is capable of receiving a cryogenic liquid, and wherein the heat engine is operable to create energy from a temperature differential between the ambient waters and the cryogenic liquid; a working fluid for operation within the heat engine under system temperatures and conditions; a riser operable to deliver the seawater to the working fluid evaporator; a power conduit to deliver the energy produced by the heat engine to a predetermined destination; and a pipeline to deliver regasified cryogenic product to a delivery destination.
 2. The system of claim 1, wherein cryogenic liquid comprises liquid natural gas.
 3. The system of claim 1, wherein the liquid heat source comprises ambient seawater.
 4. The system of claim 1, wherein the working fluid comprises ammonia.
 5. The system of claim 1, wherein the heat engine further comprises a separator.
 6. The system of claim 5, wherein the heat engine further comprises a recuperator.
 7. The system of claim 1, wherein the heat engine comprises a Rankine cycle.
 8. The system of claim 1, wherein the heat engine comprises a Kalina cycle.
 9. A regasification process for a cryogenic liquid comprising the steps of: providing the cryogenic liquid at a temperature of about −160° C. or below; providing a working fluid; providing a heat engine operatively connected to a pumping system, wherein the heat engine comprises a working fluid evaporator and a working fluid condenser, wherein the working fluid evaporator is capable of receiving a liquid heat source, wherein the working fluid condenser is capable of receiving a cryogenic liquid, and wherein the heat engine is operable to create energy from a temperature differential between the liquid heat source and the cryogenic liquid; presenting the cryogenic liquid to the heat engine and converting the cryogenic liquid into regasified cryogenic product; delivering the energy to a predetermined destination; and delivering the regasified cryogenic product to a predetermined destination.
 10. The method of claim 9, wherein the liquid heat source comprises ambient seawater.
 11. The method of claim 9, wherein the working fluid comprises a refrigerant.
 12. The method of claim 11, wherein the refrigerant comprises ammonia, an organic fluid, or a mixture thereof.
 13. The method of claim 9, wherein the working fluid comprises a binary liquid.
 14. The method of claim 9, wherein the heat engine further comprises a separator.
 15. The method of claim 14, wherein the heat engine further comprises a recuperator.
 16. The method of claim 9, wherein the heat engine comprises a Rankine cycle.
 17. The method of claim 9, wherein the heat engine comprises a Kalina cycle. 